1. Field of the Invention
The present invention relates to an electronic apparatus, such as a video camera or a digital camera, that employs a fuel cell device as a power source, and a fuel cell control method for an electronic apparatus.
2. Description of the Related Art
For electronic apparatuses such as video cameras, rechargeable secondary batteries are generally employed as power sources. These secondary batteries are, for example, lithium ion secondary batteries, nickel-metal hydride batteries, nickel-cadmium batteries and lead-acid storage batteries. In many cases, for an electronic apparatus that includes a secondary battery, when the power provided by a battery is reduced during a battery-operated period, a low power display is provided via a display unit, and when the available battery power is equal to or lower than a specific level, the power is disconnected automatically.
On the other hand, fuel cells have been provided as power sources for electronic apparatuses, such as video cameras. A fuel cell is a power source wherein an electrochemical reaction is effected by typically using hydrogen as a fuel, and as a result of the reaction, electricity is generated to provide power to the device. There are several types of fuel cells that are consonant with different electrolytes or fuels that are employed. Also, a solid polymer fuel cell has become especially useful for electronic apparatus applications, such as video cameras.
Features of a solid polymer fuel cell are that a polymer electrolyte film is employed as an electrolyte, and that the operating temperature normally does not exceed 90 degrees C., which is lower than the other types of fuel cells. Therefore, an operation enabled apparatus temperature is quickly reached, and accordingly, the time required for activation is short, so that a solid polymer fuel cell is appropriate for an application where run and halt operations are frequently performed. Further, since the electrolyte is one formed as a thin film, the electrical resistance is low, and there is little electric loss. Therefore, the amount of power generated per unit volume can be increased, and accordingly, the entire size of an apparatus can be reduced.
For a mobile electronic apparatus for which a reduction in the size and the weight of a fuel cell is requested, the use of a large hydrogen tank or a heavy hydrogen absorbed alloy is difficult. Therefore, rather than directly using hydrogen, it is considered that the use of a methanol liquid is more proper. For the employment of methanol, two methods have been proposed: (1) a direct methanol method for supplying methanol directly to a fuel cell; and (2) a methanol reformation method for extracting hydrogen, prepared from methanol, by using a reformation device and supplying the hydrogen to the fuel cell.
In a conventional example, as previously described, a mobile electronic apparatus is disclosed that includes a controller for maintaining the temperature of a fuel cell within an operating temperature band where the fuel cell can be appropriately operated (see Japanese Patent Laid-Open Publication No. 2004-87170). Further, a technique is disclosed according to which a unit, for displaying the remaining available power of a secondary battery, is provided for an electronic apparatus that uses both a fuel cell and a secondary battery. When the fuel cell needs to be recharged, a notification is provided for a user, and the usability is improved (see Japanese Patent Laid-Open Publication No. 2003-303609).
As described above, it is anticipated that a fuel cell will be employed as the power source for an electronic apparatus; however, in this case, since heat is generated during power generation, special care must be given to ensuring the operational safety.
The amount of heat generated by a device within an electronic apparatus, especially a device such as an LSI, is increased due to the high integration that is employed, and the internal apparatus temperature tends to be elevated. Thus, when a fuel cell, which may be considered as a new heat generation source, is added, the temperature within the electronic apparatus is raised. Thus, the additional source of heat may adversely affect proper function of the apparatus.
For example, in a case where for an image pickup apparatus that includes a CCD as an image pickup device, the temperature exceeds a specific level, a pixel defect may occur because of the characteristics of the CCD. Such a defect is called a white scratch because it appears that white light is being emitted, and for a screen display, this is a quality defect.
Further, most individual operating devices include LSIs or other electronic components which have heat endurance limitations, and when the temperature in the apparatus with such components is raised excessively, function failures may occur.
In addition, when magnetic tape is employed for recording/reproduction, temperature dependant characteristics, related to the type of tape material and the method by which magnetic powder is applied to this material, contribute to such deterioration as the easy scratching of tape, which can occur at high temperatures.
Above all, since when a mobile apparatus is employed it is held in a user's hand, the excessive generation of heat during operation can discomfort a user, and can considerably degenerate the usability of the apparatus.
As described above, while a fuel cell can perhaps be inconvenient, in that the internal temperature of an apparatus is increased, at high temperatures, the reaction of the fuel cell is advanced and the functioning of the fuel cell is improved. Therefore, for the use of a fuel cell for an electronic apparatus, temperature management is very important.